1. Field of Invention
This disclosure generally relates to process characterization, monitoring and control of semiconductor substrates with a focused laser beam in conjunction with laser and other processing methods.
2. Related Art
A number of techniques are available for chemical analysis of in situ semiconductor processes that incorporate some form of spectroscopy to assess species concentrations affecting the process. While each may have particular advantages, there are also disadvantages whereby incorporation of the method in situ is difficult or not possible. In many cases, evacuated chamber low pressure operation is required. In addition, many such processes are destructive of at least portions of the substrate, and therefore may not enable comprehensive mapping of process characterization. For example, inductively coupled plasma mass spectroscopy (ICP-MS) requires low pressure plasma discharge to enable mass spectroscopy. Glow discharge mass spectroscopy (GDMS) also requires low pressure. In addition, the sample must either be conductive or requires a conductive coating, which complicates process analysis and fabrication. Sputtering Optical emission spectroscopy (SOES) requires low pressure operation to sputter material for depth profiling. Auger electron spectroscopy (AES), secondary ion mass spectroscopy (SIMS), and X-ray photoelectron spectroscopy (XPS) also all require low pressure for material sputtering and mass spectroscopy. The analytical sensor systems mentioned above all require complex low pressure environments and involve some form of mass transfer (i.e., sputtering, mass spectroscopy) or X-ray production equipment. All-optical techniques may be easier to implement, requiring access to the process environment only through transparent windows or via optical fiber, and therefore are not required to be vacuum-compatible. Additionally, an optical method of spectroscopy that does not also require some form of excitation beyond that which results in the normal course of processing would be advantageous.
Focused laser beams have found applications in drilling, scribing, and cutting of semiconductor wafers, such as silicon. Marking and scribing of non-semiconductor materials, such as printed circuit boards and product labels are additional common applications of focused laser beams. Micro-electromechanical systems (MEMS) devices are laser machined to provide channels, pockets, and through features (holes) with laser spot sizes down to 5 μm and positioning resolution of 1 μm. Channels and pockets allow the device to flex. All such processes rely on a significant rise in the temperature of the material in a region highly localized at the laser beam point of focus.
The foregoing applications, however, are all, to some degree, destructive, and relate generally to focused laser beams at power densities intended to ablate material. Thus, there is a need to provide and control laser beams to achieve process monitoring for electronic and/or optical device fabrication on semiconductor wafers that are non-destructive, and which do not interfere with, or are compatible with other laser-based and/or non-laser manufacturing processes.